Polarizing plate protection film, polarizing plate, and liquid crystal display device

Abstract

A polarizing plate protection film and a polarizing plate which can restrain generation of rainbow-like irregularities and enables to produce an excellent quality liquid crystal display device when a commercially-available film is used as it is under commercially-available conditions or when a film produced by a common film forming method is used. The polarizing plate protection film includes: a transparent substrate; and a refractive index difference-mitigating part formed on the transparent substrate and provided with a low refractive index layer at its most outer layer, in which the low refractive index layer has a refractive index to the light transmitted through the transparent substrate smaller than that of the transparent substrate and bigger than that of the air. An in-plane distribution of the in-plane retardation (Re) of the transparent substrate is 5 nm or more.

What is clamed is: 
     
       1. A polarizing plate protection film comprising:
 a transparent substrate; and 
 a refractive index difference-mitigating part formed on the transparent substrate and provided with a low refractive index layer at its most outer layer, in which the low refractive index layer has a refractive index to a light transmitted through the transparent substrate smaller than a refractive index of the transparent substrate and bigger than a refractive index of air, 
 wherein an in-plane distribution of an in-plane retardation (Re) of the transparent substrate is 5 nm or more, and 
 wherein a difference between a reflectance of P wave and a reflectance of S wave at incident angle of 50 degrees is 20% or less. 
 
     
     
       2. A polarizing plate protection film comprising:
 a transparent substrate; and 
 a refractive index difference-mitigating part formed on the transparent substrate and provided with a low refractive index layer at its most outer layer, in which the low refractive index layer has a refractive index to a light transmitted through the transparent substrate smaller than a refractive index of the transparent substrate and bigger than a refractive index of air, 
 wherein an in-plane distribution of an in-plane retardation (Re) of the transparent substrate is 5 nm or more, and 
 wherein the refractive index difference-mitigating part has a reflectance to the light transmitted through the transparent substrate at Brewster's angle of 6% or more, and wherein a difference between a reflectance of P wave and a reflectance of S wave at incident angle of 50 degrees is 20% or less as the polarizing plate protection film. 
 
     
     
       3. The polarizing plate protection film according to  claim 1 , wherein the refractive index difference-mitigating part is formed only by the low refractive index layer. 
     
     
       4. The polarizing plate protection film according to  claim 1 , wherein a value of the in-plane retardation (Re) of the transparent substrate is 1300 nm or more. 
     
     
       5. The polarizing plate protection film according to  claim 1 , wherein the transparent substrate is made of polyethylene terephthalate (PET). 
     
     
       6. A polarizing plate comprising:
 a first polarizing plate protection film; 
 a polarizer; and 
 a second polarizing plate protection film, 
 wherein the first polarizing plate protection film further comprises a transparent substrate, and a refractive index difference-mitigating part formed on the transparent substrate and provided with a low refractive index layer at its most outer layer, in which the low refractive index layer has a refractive index to a light transmitted through the transparent substrate smaller than a refractive index of the transparent substrate and bigger than a refractive index of air, and an in-plane distribution of an in-plane retardation (Re) of the transparent substrate is 5 nm or more, 
 wherein the polarizer is laminated on the transparent substrate of the first polarizing plate protection film, 
 wherein the second polarizing plate protection film is laminated on the polarizer, and 
 wherein the first polarizing plate protection film is a film wherein a difference between a reflectance of P wave and a reflectance of S wave at incident angle of 50 degrees is 20% or less. 
 
     
     
       7. A liquid crystal display device comprising:
 a liquid crystal cell; 
 a display-side polarizing plate provided to one side of the liquid crystal cell; and 
 a backlight-side polarizing plate provided to the other side of the liquid crystal cell, 
 wherein the display-side polarizing plate further comprises: a first polarizing plate protection film, a polarizer, and a second polarizing plate protection film, 
 wherein the first polarizing plate protection film comprises a transparent substrate, and a refractive index difference-mitigating part formed on the transparent substrate and provided with a low refractive index layer at its most outer layer, in which the low refractive index layer has a refractive index to a light transmitted through the transparent substrate smaller than a refractive index of the transparent substrate and bigger than a refractive index of air, and an in-plane distribution of an in-plane retardation (Re) of the transparent substrate is 5 nm or more; the polarizer is laminated on the transparent substrate of the first polarizing plate protection film, the second polarizing plate protection film is laminated on the polarizer, and the first polarizing plate protection film is a film wherein a difference between a reflectance of P wave and a reflectance of S wave at incident angle of 50 degrees is 20% or less. 
 
     
     
       8. The polarizing plate protection film according to  claim 2 , wherein the refractive index difference-mitigating part is formed only by the low refractive index layer. 
     
     
       9. The polarizing plate protection film according to  claim 2 , wherein a value of the in-plane retardation (Re) of the transparent substrate is 1300 nm or more. 
     
     
       10. The polarizing plate protection film according to  claim 2 , wherein the transparent substrate is made of polyethylene terephthalate (PET).